The present invention relates to novel rare earth magnets, and more particularly to high-performance permanent magnet materials based on FeBR systems which do not necessarily contain relatively scarce rare earth metals such as Sm, and are mainly composed of Fe and relatively abundant light rare earth elements, particularly Nd and Pr, which may find less use, and a process for the preparation of the same.
Permanent magnet materials are one of the important electric and electronic materials used in extensive areas ranging from various electrical appliances for domestic use to peripheral terminal devices for large-scaled computers. There has recently been an increasing demand for further upgrading of the permanent magnet materials in association with needs for miniaturization and high efficiency of electrical equipment. Magnet materials having high coercive forces have also been required in many practical fields such as, for instance, those for motors, generators and magnetic couplings.
Typical of the permanent magnets currently in use are alnico, hard ferrite and rare earth/cobalt magnets. Among these, the rare earth/cobalt magnets have taken the place of permanent magnets capable of meeting high magnet properties now required. However, the rare earth/cobalt magnets are very expensive due to the requirement of relatively scarce Sm and the uncertain supply of Co which is used in larger amounts.
To make is possible to use extensively the rare earth magnets in wider ranges, it is desired to mainly use light rare earth metals contained abundantly in ores as the rare earth elements and to avoid the use of much Co that is expensive.
In an effort to obtain such permanent magnet materials, R-Fe.sub.2 base compounds, wherein R is at least one of the rare earth metals, have been investigated. A. E. Clark has discovered that sputtered amorphous TbFe.sub.2 has an energy product of 29.5 MGOe at 4.2 degrees K., and shows a coercive force Hc=3.4 kOe and a maximum energy product (BH)max=7 MGOe at room temperature upon heat-treated at 300-500 degrees C. Reportedly, similar investigation on SmFe.sub.2 indicated that 9.2 MGOe was reached at 77 degrees K. However, these materials are all obtained by sputtering in the form of thin films that cannot be generally used as magnets for, e.g., speakers or motors. It has further been reported that melt-quenched ribbons of PrFe base alloys show a coercive force Hc of as high as 2.8 kOe.
In addition, Koon et al discovered that, with melt-quenched amorphous ribbons of (Fe.sub.0.82 B.sub.0.18).sub.0.9 Tb.sub.0.05 La.sub.0.05, Hc of 9 kOe was reached upon annealing at 627 degrees C. (Br=5 kG). However, (BH)max is then low due to the unsatisfactory loop squareness of the magnetization curves (N. C. Koon et al, Appl. Phys. Lett. 39 (10), 1981, pp.840-842).
Moreover, L. Kabocoff et al reported that among melt-quenched ribbons of (Fe.sub.0.8 B.sub.0.2).sub.1-x Pr.sub.x (x=0-0.03 atomic ratio) certain ones of the Fe-Pr binary system show Hc on the kilo oersted order at room temperature.
These melt-quenched ribbons or sputtered thin films are not practical permanent magnets (bodies) that can be used as such. It would be practically impossible to obtain practical permanent magnets from these ribbons or thin films.
That is to say, no bulk permanent magnet bodies of any desired shape and size are obtainable from the conventional Fe-B-R base melt-quenched ribbons or R-Fe base sputtered thin films. Due to the unsatisfactory loop squareness (or rectangularity) of the magnetization curves, the Fe-B-R base ribbons heretofore reported are not taken as practical permanent magnet materials comparable with the conventional, ordinary magnets. Since both the sputtered thin films and the melt-quenched ribbons are magnetically isotropic by nature, it is indeed almost impossible to obtain therefrom magnetically anisotropic (hereinbelow referred to "anisotropic") permanent magnets for the practical purpose.